Awards:American Council of Engineering Companies, NC, Award of Excellence

Programmatic Permitting Services for Land Application of Wastewater from Hydro-Demolition and Diamond Grinding of Concrete

S&ME assisted the North Carolina Department of Transportation (NCDOT) to develop an environmentally sustainable approach to managing concrete byproducts. Hydrodemolition and diamond grinding operations are prevalent in bridge maintenance and concrete roadway projects. The typical approach is to dispose byproducts generated from these processes in wastewater treatment facilities and landfills. These remedies, however, impose a substantial cost. Working in collaboration, the team developed a program to permit and beneficially reuse these byproducts. Specifically, the program involved the land application of hydrodemolition runoff water (HRW) and diamond grinding slurries (DGS) onto NCDOT properties and private farmland.

Land application of the concrete residuals requires a permit. The North Carolina Department of Environment and Natural Resources (NCDENR), however, did not have a specific permitting process for land application of HRW and DGS. Therefore, the team tailored the Residuals Management permit process to meet this unique need. To acquire the NCDENR permit, the team needed to demonstrate that land application is beneficial. This required coordinated research performed by North Carolina State University to evaluate soil pH reactions and determine liming values of HRW and DGS.

The research showed substantial benefits from the land application of concrete byproducts. The residuals can adjust soil pH. For farmers, this offered a significant cost-saving process from traditional application of lime to achieve the same amended soil. In addition, the soil pH adjustment helps prevent leaching of nutrients and the potential for agricultural runoff, thus protecting surface water and groundwater resources. NCDOT realized immediate cost savings through elimination of costly wastewater treatment and landfill disposal charges. Most important, these benefits can be applied to other transportation uses as well.

NCDOT utilized the new permitting process on the new Western Wake Expressway in Wake County. The diamond grinding process was used on the concrete for the entire length of the project. The hydro-demolition runoff water and the diamond grinding slurry both have a high pH and are beneficial to soils for pH adjustment. S&ME is assisting the NCDOT with the permitting and the land application of these products on highway right-of-ways and medians. Permits are obtained from the Division of Water Quality (DWQ) Land Application Unit (LAU). This was a new permitting process for both NCDOT and the DWQ-LAU.